1. Field of the Invention
This application relates to electrical enclosures. More particularly, it concerns such HF (high frequency) shielded metal electrical enclosures for assembling with electronic components.
2. Description of the Prior Art
Electrical enclosures for assembling with electronic components typically consist of an enclosure bottom and a lid. The enclosure bottom usually is designed with 2 to 4 mounting holes for the enclosure itself outside of the enclosure interior and also has 2 to 6 threads for fastening the lid to the bottom, e.g., see U.S. Pat. No. 4,632,269, the disclosure of which is incorporated herein by reference.
The lids of these electrical enclosures have to be closed by screws or quick fasteners to make sure that no dust, humidity, oil and water can enter the enclosure interior. For this, the enclosure bottom typically has a tongue and the lid has a groove and the groove takes a gasket of rubber or plastic. After assembling, the tongue presses against the gasket to seal the enclosure lid to the bottom.
Because more and more microelectronic components are used in all kind of industrial fields there is a big risk, they will influence and disturb each other. The designer has to take care, to protect his products from being influenced by other components or against disturbing other electronic components with his own product. This interference problem is of such importance and magnitude that governmental regulations are in effect or pending relating thereto.
The manufacturers of electrical enclosures are well aware of the need for HF shielding and a variety of schemes have been developed, both for metal and plastic enclosures, for providing such articles of manufacture with HF shielding properities, e.g., see U.S. Pat. Nos. 2,317,813; 3,534,146; 4,155,478; 4,964,018; and 5,095,177.
Aluminium enclosures of standard design give some protection against HF interferences with enclosed components because of the nature of metal, but no normally used plastic material has any shielding ability. In many cases, particularly with high frequency radiations, enclosures made of aluminium metal can provide adequate HF shielding. With lower frequency radiations, HF shielding becomes a more serious problem. For example, conventional groove and tongue sealing structures have to be free of paint and expensive contacting gaskets have to be installed.
An apparent way to enhance the shielding capability of enclosures is to create paint-free contact areas, but this succeeds only when the contact areas are protected against corrosion. Otherwise, the contact areas will after a short time corrode and the HF screening effect is lost.
With prior known electrical enclosures, the contact between the lid and the bottom can be made only on the outer areas of the enclosure, i.e., only in the outer areas is the contact metal to metal, but this area is not protected against corrosion. It is also very costly, to hold this area free of paint, but the majority of elecrical enclosure users want them painted on the outside for corrosion-protection and for decorative reasons. Because of this, the use of costly contacting gaskets and paintfree tongues and grooves has been the only effective method available, but even with this solution, corrosion problems exist.
The present invention provides new improved forms of HF shielding electrical enclosures that address and mitigate the problems discussed above associated with related electrical enclosures available heretofore.